198 research outputs found
Chandra and Hubble Study of a New Transient X-ray Source in M31
We present X-ray and optical observations of a new transient X-ray source in
M31 first detected 23-May-2004 at R.A.=00:43:09.940 +/- 0.65'',
Dec.=41:23:32.49 +/- 0.66''. The X-ray lightcurve shows two peaks separated by
several months, reminiscent of many Galactic X-ray novae. The location and
X-ray spectrum of the source suggest it is a low mass X-ray binary (LMXB).
Follow-up HST ACS observations of the location both during and after the
outburst provide a high-confidence detection of variability for one star within
the X-ray position error ellipse. This star has B ~ 1 mag, and there is
only a ~1% chance of finding such a variable in the error ellipse. We consider
this star a good candidate for the optical counterpart of the X-ray source. The
luminosity of this candidate provides a prediction for the orbital period of
the system of 2.3 days.Comment: 17 pages, 3 figures, 4 tables, accepted for publication in Ap
Optical Constraints on an X-ray Transient Source in M31
We have detected a transient X-ray source in the M31 bulge through a
continuing monitoring campaign with the Chandra ACIS-I camera. The source was
detected at R.A.=00:42:33.428 +/- 0.11'', Dec.=+41:17:03.37 +/- 0.11'' in only
a single observation taken 2004 May 23. Fortuitous optical HST/ACS imaging of
the transient location prior to the X-ray outburst, along with follow-up
HST/ACS imaging during and after the outburst, reveals no transient optical
source brighter than B (equivalent) = 25.5. The location of the source and its
X-ray properties suggest it is a low mass X-ray binary (LMXB). Assuming the
transient is similar to many Galactic X-ray novae, the X-ray luminosity of (3.9
+/- 0.5) X 10 erg s and the upper-limit on the optical luminosity
provide a prediction of <1.6 days for the orbital period of the binary system.Comment: 15 pages, 3 figures, accepted for publication in Ap
A Soft X-ray Transient in the M31 Bulge
We have examined a probable soft X-ray transient source in the M31 bulge at
R.A.=0:42:41.814 +/- 0.08", Dec. = 41:16:35.86 +/- 0.07". On the three
occasions we observed the source, its spectrum was soft (kT_{in} ~1 keV). The
brightest detection of the source was 2004 July 17 with a 0.3-7 keV luminosity
of ~5 X 10^{37} erg/s. The only previous detection of the source was in 1979 by
the Einstein observatory. The multiple detections over 25 years suggest the
duty cycle of the source is in the range 0.02-0.06. Coordinated HST/ACS imaging
before, during, and after the outburst revealed no variable optical source
within the position errors of the X-ray source. The optical data place a firm
upper limit on the brightness of the counterpart of the X-ray outburst of
B>24.7, suggesting the binary has a period <5.2 days. The X-ray spectrum and
lack of bright stars at the source location indicate the source was a soft
transient event occurring in a low-mass X-ray binary, making this source a good
black hole candidate in M31.Comment: 18 pages, 4 tables, 3 figures, accepted for publication in Ap
Angiotensin II stimulates superoxide production by nitric oxide synthase in thick ascending limbs
Angiotensin II (Ang II) causes nitric oxide synthase (NOS) to become a source of superoxide (O2 (-)) via a protein kinase C (PKC)-dependent process in endothelial cells. Ang II stimulates both NO and O2 (-) production in thick ascending limbs. We hypothesized that Ang II causes O2 (-) production by NOS in thick ascending limbs via a PKC-dependent mechanism. NO production was measured in isolated rat thick ascending limbs using DAF-FM, whereas O2 (-) was measured in thick ascending limb suspensions using the lucigenin assay. Consistent stimulation of NO was observed with 1 nmol/L Ang II (P \u3c 0.001; n = 9). This concentration of Ang II-stimulated O2 (-) production by 50% (1.77 ± 0.26 vs. 2.62 ± 0.36 relative lights units (RLU)/s/μg protein; P \u3c 0.04; n = 5). In the presence of the NOS inhibitor L-NAME, Ang II-stimulated O2 (-) decreased from 2.02 ± 0.29 to 1.10 ± 0.11 RLU/s/μg protein (P \u3c 0.01; n = 8). L-arginine alone did not change Ang II-stimulated O2 (-) (2.34 ± 0.22 vs. 2.29 ± 0.29 RLU/s/μg protein; n = 5). In the presence of Ang II plus the PKC α/β1 inhibitor Gö 6976, L-NAME had no effect on O2 (-) production (0.78 ± 0.23 vs. 0.62 ± 0.11 RLU/s/μg protein; n = 7). In the presence of Ang II plus apocynin, a NADPH oxidase inhibitor, L-NAME did not change O2 (-) (0.59 ± 0.04 vs. 0.61 ± ×0.08 RLU/s/μg protein; n = 5). We conclude that: (1) Ang II causes NOS to produce O2 (-) in thick ascending limbs via a PKC- and NADPH oxidase-dependent process; and (2) the effect of Ang II is not due to limited substrate
An X-ray Transient and Optical Counterpart in the M31 Bulge
We have obtained snapshot images of a transient X-ray source in M31 from
Chandra ACIS-I and the Hubble Space Telescope (HST) Advanced Camera for Surveys
(ACS). The Chandra position of the X-ray nova was R.A.=00:42:56.038 +/-0.08'',
Dec.=+41:12:18.50 +/-0.07''. The transient was active for at least 6 months.
Previous observations set an upper limit before the X-ray outburst,
demonstrating variability by a factor of >100 and confirming the transient
nature of the source. For the first 6 months after the initial detection, the
X-ray luminosity was ~6 X 10 erg/s; it then decayed to <5 X 10
erg/s over the following 2 months. An HST observation 29 days after the initial
X-ray detection revealed a source at R.A.=00:42:56.042, Dec.=+41:12:18.45 that
was B=24.52 +/- 0.07. This optical source faded to B=24.95 +/- 0.08^{+12}_{-5}$ days for the system.Comment: 16 pages, 4 tables, 2 figures, accepted for publication in Ap
Why are X-ray sources in the M31 Bulge so close to Planetary Nebulae?
We compare a deep (37 ks) Chandra ACIS-S image of the M31 bulge to deep [O
III] Local Group Survey data of the same region. Through precision image
alignment using globular cluster X-ray sources, we are able to improve
constraints on possible optical/X-ray associations suggested by previous
surveys. Our image registration allows us to rule out several emission-line
objects, previously suggested to be the optical counterparts of X-ray sources,
as true counterparts. At the same time, we find six X-ray sources peculiarly
close to strong [O III] emission-line sources, classified as planetary nebulae
(PNe) by previous optical surveys. Our study shows that, while the X-rays are
not coming from the same gas as the optical line emission, the chances of these
six X-ray sources lying so close to cataloged PNe is only ~1%, suggesting that
there is some connection between these [O III] emitters (possibly PNe) and the
X-ray sources. We discuss the possibility that these nebulae are misidentified
supernova remnants, and we rule out the possibility that the X-ray sources are
ejected X-ray binaries. There is a possibility that some cases involve a PN and
an LMXB that occupy the same undetected star cluster. Beyond this unconfirmed
possibility, and the statistically unlikely one that the associations are
spatial coincidences, we are unable to explain these [O III]/X-ray
associations.Comment: 21 pages, 3 figures, 2 tables, accepted for publication in A
Creative learning conversations: producing living dialogic spaces
publication-status: Publishedtypes: ArticleBackground ‘Creative learning conversations’, are methodological devices developed in two co-participative qualitative research projects exploring creativity and educational futures at the University of Exeter in England. Sources of evidence Framed by Critical Theory, the projects, one on dance education partnership, the other on student voice and transformation, sought to open space between creativity and performativity to initiate emancipatory educational change. This was undertaken over the course of five years in English primary and secondary schools, prioritising humanising, wise creativity (Chappell, 2008; Craft, 2008). Purpose This paper re-analyses data and methodological processes to characterise and theorise creative learning conversations in terms of social spatiality and dialogue. The characteristics are: partiality, emancipation, working from the ‘bottom up’, participation, debate and difference, openness to action, and embodied and verbalised idea exchange. Main argument This re-analysis theoretically adapts Bronfenbrenner’s (1979) ecological model to situate layered engagement. Utilising Lefebvre’s (1991) conceptualisation of Lived space and Bakhtin’s (1984) work on open-ended dialogue, the paper theorises creative learning conversations as producing living dialogic spaces. Conclusions Creative learning conversations are a way of contributing to change which moves us towards an education future fit for the twenty-first century. From a living dialogic space perspective a creative learning conversation is the ongoing process without forced closure of those in the roles of University academic, teachers, artists, students co-participatively researching and developing knowledge of their ‘lived space’ together. Given traditional lethargy in the educational system as a whole commitment to changing education for better futures demands active involvement in living dialogic space, where our humanity both emerges from and guides our shared learning
Introduction: reconsidering the region in India: mobilities, actors and development politics
In this introduction to a special issue on ‘Reconsidering the Region in India’, we aim to develop a synthetic and theoretically nuanced account of the multifarious ways in which the idea of region has been imbricated in diverse spatial, political, cultural and socio-economic configurations. We draw from various bodies of anthropological, geographic and historical literature to elaborate on three themes that we believe are central to understanding contemporary processes of region-making in India: trans-regional mobilities and connections; the actors who produce and perform regional imaginaries; and changing regional politics of development.IS
Sensitivity and specificity of monoclonal and polyclonal immunohistochemical staining for West Nile virus in various organs from American crows (Corvus brachyrhynchos)
<p>Abstract</p> <p>Background</p> <p>Based on results of earlier studies, brain, heart and kidney are most commonly used for West Nile virus (WNV) detection in avian species. Both monoclonal and polyclonal antibodies have been used for the immunohistochemical diagnosis of WNV in these species. Thus far, no studies have been performed to compare the sensitivity and specificity of monoclonal and polyclonal antibodies in detecting WNV in American crows (<it>Corvus brachyrhynchos</it>). Our objectives were to determine 1) the comparative sensitivities of monoclonal and polyclonal antibodies for immunohistochemical (IHC) diagnosis of WNV infection in free-ranging American crows, 2) which organ(s) is/are most suitable for IHC-based diagnosis of WNV, and 3) how real-time RT-PCR on RNA extracted from formalin-fixed paraffin-embedded tissues compared to IHC for the diagnosis of WNV infection.</p> <p>Methods</p> <p>Various combinations, depending on tissue availability, of sections of heart, kidney, brain, liver, lung, spleen, and small intestine from 85 free-ranging American crows were stained using a rabbit-polyclonal anti-WNV antibody as well as a monoclonal antibody directed against an epitope on Domain III of the E protein of WNV. The staining intensity and the extent of staining were determined for each organ using both antibodies. Real-time RT-PCR on formalin-fixed paraffin-embedded tissues from all 85 crows was performed.</p> <p>Results</p> <p>Forty-three crows were IHC-positive in at least one of the examined organs with the polyclonal antibody, and of these, only 31 were positive when IHC was performed with the monoclonal antibody. Real-time RT-PCR amplified WNV-specific sequences from tissue extracts of the same 43 crows that were IHC-positive using the polyclonal antibody. All other 42 crows tested negative for WNV with real-time PCR and IHC staining. Both antibodies had a test specificity of 100% when compared to PCR results. The test sensitivity of monoclonal antibody-based IHC staining was only 72%, compared to 100% when using the polyclonal antibody.</p> <p>Conclusion</p> <p>The most sensitive, readily identified, positively staining organs for IHC are the kidney, liver, lung, spleen, and small intestine. Real-time RT-PCR and IHC staining using a polyclonal antibody on sections of these tissues are highly sensitive diagnostic tests for the detection of WNV in formalin-fixed tissues of American crows.</p
The Magellan-TESS Survey I: Survey Description and Mid-Survey Results
One of the most significant revelations from Kepler is that roughly one-third
of Sun-like stars host planets which orbit their stars within 100 days and are
between the size of Earth and Neptune. How do these super-Earth and sub-Neptune
planets form, what are they made of, and do they represent a continuous
population or naturally divide into separate groups? Measuring their masses and
thus bulk densities can help address these questions of their origin and
composition. To that end, we began the Magellan-TESS Survey (MTS), which uses
Magellan II/PFS to obtain radial velocity (RV) masses of 30 transiting
exoplanets discovered by TESS and develops an analysis framework that connects
observed planet distributions to underlying populations. In the past, RV
measurements of small planets have been challenging to obtain due to the
faintness and low RV semi-amplitudes of most Kepler systems, and challenging to
interpret due to the potential biases in the existing ensemble of small planet
masses from non-algorithmic decisions for target selection and observation
plans. The MTS attempts to minimize these biases by focusing on bright TESS
targets and employing a quantitative selection function and multi-year
observing strategy. In this paper, we (1) describe the motivation and survey
strategy behind the MTS, (2) present our first catalog of planet mass and
density constraints for 25 TESS Objects of Interest (TOIs; 20 in our population
analysis sample, five that are members of the same systems), and (3) employ a
hierarchical Bayesian model to produce preliminary constraints on the
mass-radius (M-R) relation. We find qualitative agreement with prior
mass-radius relations but some quantitative differences (abridged). The the
results of this work can inform more detailed studies of individual systems and
offer a framework that can be applied to future RV surveys with the goal of
population inferences.Comment: 101 pages (39 of main text and references, the rest an appendix of
figures and tables). Submitted to AAS Journal
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